1. Field of the Invention
The present invention relates to an imprint technique used for manufacturing information recording apparatuses, and particularly to an imprint apparatus and a method for imprinting for the processing of magnetic recording media.
2. Description of the Related Art
In recent years, information recording apparatuses used in general purpose computers or the like have dealt with high capacity data including audio, video and the like, and the recording capacities thereof have thus been increased. With regard to the magnetic recording medium of hard disks and the like serving information recording apparatuses, “patterned media” has been considered favorable. In this patterned media, in order to increase the recording capacity, a magnetic layer on the medium's surface is physically patterned so that tracks or recording bits are physically isolated from each other. The recording density of the patterned media is expected to be 500 gigabit/square inch (Gbpsi), and the period of neighboring recording bits is about 30 nm or smaller. A magnetic recording medium at the above size cannot be fabricated by using earlier photolithography due to limits on the wavelength of light. It is possible to microfabricate the magnetic recording medium in the above size by using electron beam lithography, focused ion beam lithography or the like. However, poor throughput becomes a problem.
Therefore, imprinting is employed, where a resist film applied onto a magnetic layer is physically pressed by using a stamper made from a master-processing disk produced in nanoscale by electron beam lithography or the like. Thus, a pattern of projections and recesses on the surface of the stamper is transferred onto the resist film. Thereafter, etching is performed using the pattern of projections and recesses on the resist film as a mask so that the magnetic layer is patterned.
Imprinting mainly includes “2P method”, “hot embossing method”, and “high pressure pressing method” at atmospheric pressure and room temperature. First, in 2P method, ultraviolet (UV) curing liquid resist is applied onto a substrate to be thicker than the size of the distortion of the substrate, and is pressed by a transparent stamper made of quartz or the like. Thereafter, UV light is emitted from behind the stamper's surface of projections and recesses so that the resist on the substrate is cured. By doing so, the resist in contact with the stamper's surface is also cured. Thus a resist film onto which the projections and recesses of the stamper's surface are transferred is obtained after the stamper is removed.
For hot embossing method, a non-transparent stamper made of metal or the like is prepared. Resist applied onto a substrate is pressed by the stamper, and the substrate, resist and stamper are heated to the glass transition temperature of the resist or higher while they are pressed. The resist sandwiched between the substrate and stamper thus becomes soft and the shape of the stamper's surface is transferred onto the resist. Thereafter, the substrate, resist and stamper are cooled while being pressed. When the substrate, resist and stamper are at or below the glass transition temperature, the stamper is removed. Thus, projections and recesses on the stamper's surface are transferred onto the resist film.
For high pressure pressing method at atmospheric pressure and room temperature, a non-transparent stamper made of metal or the like is prepared. Resist having the lowest possible glass transition temperature is applied onto a substrate. The resist is then pressed by the imprint stamper at a pressure of 10 MPa or higher. The favorable glass transition temperature of the resist is 50° C. or lower. This low glass transition temperature enables high pressure pressing method even at room temperature, and thereby projections and recesses on the stamper's surface are transferred onto the resist film.
It is difficult, with imprinting, to uniformly press a large area because of the distortions of the substrate and the stamper, or the like. In 2P method described earlier, a thick resist film is used. Therefore, projections and recesses on the stamper's surface can be transferred onto the resist film regardless of the distortion of the substrate. However, the distortions of both the stamper and the surface of the substrate do not sufficiently offset one another. Hence, the distortions eventually emerge as film thickness variations of the resist film sandwiched between the substrate and the stamper.
In hot embossing method, the shape of the resist surface after imprinting is stable, since resist is hard when it has cooled down to the glass transition temperature or lower. However, heating and cooling processes are added, causing poor throughput. In addition, the problem of irregular imprinting caused by the distortions of the substrate and stamper or the like remains unsolved.
In high pressure pressing method at atmospheric pressure and room temperature, distortions of the substrate and stamper are corrected by high pressure pressing method, enabling uniform imprinting of a large area. However, since the resist is deformed at room temperature, distortion of the resist's surface after imprinting occurs over time. Therefore, a material having not only characteristics of low glass transition temperature but also UV curing characteristics is used for the resist, and a UV curing process is performed on the resist surface after imprinting in order to suppress deformation of the resist's surface over time. However, since the gradual deformation of the resist's surface begins immediately after imprinting, the shape of resist surface will have already changed by the time the UV curing process is performed. The resist can be cured while pressing if a stamper made of a transparent material such as quartz can be used like 2P method. However, such transparent materials have problems with strength when being pressed under a high pressure and thus cannot be used.